Basic research on protein structure, function, and regulation has produced the following results: (1) Heat-induced reversible partial unfolding of dodecameric Mn.glutamine synthetase (Mn.GS) from Escherichia coli at pH 7 has been studied by spectral techniques and by differential scanning calorimetry (DSC). A single endotherm for two two-state transitions with a calorimetric delta-H of 211 +/- 4 kcal/(mol dodecamer) was observed. Cooperative interactions apparently link partial unfolding reactions of all subunits within the GS dodecamer. Variable effects of active-site ligands can be described in thermodynamic terms. (2) The thermal denaturation of the tryptophan synthase complex from S. typhimurium also is being studied. DSC profiles exhibit two well resolved endotherms corresponding to thermally induced unfolding of the 2alpha and beta-beta domains in the multienzyme complex. Preliminary results indicate that the unfolding of the alpha-beta-beta-alpha complex is slowly reversible and that a pre-transition exposure of Trp residues in beta chains occurs. (3) Transcriptional factor IIIA from immature oocytes of Xenopus laevis has been specifically labeled at Cys-287 with a highly fluorescent probe (IAEDANS). Four DNA fragments from the inner control region (ICR) of the 5 S RNA gene have been labeled at 4 specific positions with fluorescent probes and purified in order to study TFIIA-DNA interactions by fluorescence resonance energy transfer and emission anisotropy techniques. In addition, wild-type and mutant forms of TFIIIA are being cloned.